Fastener driving systems (such as fastener drive tools and nail guns) are common in the construction industry. Fastener driving systems have many advantages over hammers, such as the ability to drive a fastener instantly without splitting wood, and consistently setting a nail head below a substrate. Fastener driving systems are usually driven by electromagnet(s), compressed air or a small explosive charge. These power assisted means of driving fasteners can be either in the form of finishing nail systems used in baseboards or crown molding in house and household projects, or alternatively, in the form of common nail systems used to make walls or hang sheathing onto same. Such fastener driving systems may either be portable (i.e., not connected or tethered to an air compressor or wall outlet) or non-portable.
Various concepts and components are conceded and emphasized as attempts and develops over the years in the art of fastener driving systems and similar explosively actuated equipment. The most common fastener driving system uses a source of compressed air to actuate a cylinder to push the nail into a receiving member. For applications in which portability is not required, this is a very functional system and allows rapid delivery of fasteners for quick assembly. A disadvantage of such a fastener driving system is that the user is required to purchase an air compressor and associated air lines in order to use this system. A further disadvantage is the inconvenience of being tethered through an air hose to an air compressor.
To solve the problems of fastener driving systems actuated by compressed air, several types of portable nail guns operable by fuel cells have been developed. Typically, these guns have a cylinder in which a fuel is introduced along with oxygen from the air. The subsequent mixture is ignited with the resulting expansion of gases pushing the cylinder and thus driving the nail into the substrate. However, this design is complicated and is more expensive then a standard pneumatic nail gun. Such fuel cell driven units also have certain disadvantages: the chambering of an explosive mixture of fuel; the use of consumable fuel cartridges; a loud report; and the release of combustion products.
Another commercially available fastener driving system is nail guns using electrical energy to drive a stapler or wire brad. These units typically use a solenoid to drive the fastener or a ratcheting spring system. These units have limited application to short sized fasteners, are subjected to high reactionary forces on the user, and are limited in their repetition rate. The high reactionary force is a consequence of a comparatively long time it takes to drive the fastener into the substrate. Additionally, because of the use of mechanical springs or solenoids, the ability to drive larger fasteners or longer fasteners is severely restricted, thereby relegating these units to a small niche range of applications. Further, a disadvantage of the solenoid driven units is that the above-mentioned unit must be plugged into an electrical power source in order to have enough voltage to create the force needed to drive even short fasteners.
Yet another commercially available fastener driving system is a unit working on a flywheel mechanism and an associated clutch that interacts with an anvil for driving the fastener. This unit is capable of driving fasteners very quickly and in a variety of sizes. The primary drawback to such a unit is the large weight and size as compared to the pneumatic counterpart. Additionally, the drive mechanism is very complicated in configuration, thus requiring a high retail cost in comparison to the pneumatic nail gun.
Prior art teaches several other techniques of driving a nail or staple by different fastener driving systems. One of the techniques is based on a multiple impact design. In this design, a motor or other power source is connected to the impact anvil through either a lost motion coupling or other device. This allows the power source to make multiple impacts on the nail to drive it into the substrate. The disadvantage in this design is increased operator fatigue, as the actuation technique is a series of blows rather than a single drive motion. A further disadvantage is that the multiple impact design requires the use of an energy absorbing mechanism once the nail is seated, with such mechanism being needed to prevent the anvil from causing excessive damage to the substrate as it seats the fastener. Furthermore, the multiple impact designs are not efficient because of the constant motion reversal limiting the operator production speed.
A second technique includes the use of potential energy storage mechanisms in the form of a mechanical spring. In this technique, the spring is cocked (or activated) through an electric motor. Once the spring is sufficiently compressed, the energy is released from the spring into the anvil (or nail driving piece), thus pushing the nail into the substrate. There are several drawbacks existing to this technique. First, this technique comprises a complex system of compressing and controlling the spring and in order to store sufficient energy the spring has to be very heavy and bulky. Second, the spring suffers from fatigue, which gives the tool a very short life. Furthermore, metal springs have to move a significant amount of mass in order to decompress, which results low speed nail drivers that place a high reactionary force on a user.
U.S. Pat. No. 3,589,588 to Vasku, U.S. Pat. No. 5,503,319 to Lai, and U.S. Pat. No. 3,172,121 to R. H. Doyle, et al. are the examples of the use of potential energy storage mechanisms in the form of a mechanical spring. U.S. Pat. No. 4,215,808 to Sollberger discloses an improved design, which replaces the mechanical spring with an air spring, compressing air within a cylinder, and then releasing the compressed air by use of a gear drive.
Although some of the drawbacks of the above-mentioned technique using the potential energy storage mechanisms in the form of a mechanical spring were overcome by the use of air spring, the application of air spring is subject to other limitations. The primary drawback is the safety hazard in the event of anvil jamming on the downward stroke. If the fastener jams or buckles within the feeder and an operator tries to clear the jam, the operator may be subjected to the full force of the anvil, as the anvil is predisposed to the down position. Another disadvantage is the need to feed the fastener once the anvil clears the fastener on the backward stroke, which increases the time needed to operate the device and can result in jams and poor operations, especially with longer fasteners. A further disadvantage to the air spring results from the need to have the ratcheting mechanism as part of the anvil drive. This weight causes significant problems in controlling the fastener drive since the weight must be stopped at the end of the stroke. This added mass slows the fastener drive stroke and increases the reactionary force on the operator.
Additionally, because significant kinetic energy is contained within the air spring and piston assembly, the unit suffers from poor efficiency. This technique is also subject to a complicated drive system for coupling and uncoupling the air spring and ratchet from the drive train, which increases the production cost and reduces the system reliability.
U.S. Pat. No. 5,720,423 to Kondo again discloses an air spring which is compressed and then released to drive the nail. The drive or compression mechanism used in this technique is limited in stroke and thus is limited in the amount of energy which can be stored and introduced into the air stream. In order to get sufficient energy in the air stream to achieve good performance, use of a gas supply is provided which preloads the cylinder at a pressure higher then atmospheric pressure. Furthermore, the compression mechanism is bulky and complicated. Also, the timing of the motor is complicated by the small amount of time between the release of the piston and anvil assembly from the drive mechanism and its subsequent re-engagement. The anvil begins in the retracted position, which further complicates and increases the size of the drive mechanism. Furthermore, the method of activation by compressing the air to full energy and then releasing off the tip of the gear while under full load causes severe mechanism wear.
A third technique uses flywheels as energy storage means. The flywheels are used to launch a hammering anvil impacting the nail. The examples of this design are U.S. Pat. No. 4,042,036 to Smith et al., U.S. Pat. No. 5,511,715 to Crutcher et al. and U.S. Pat. No. 5,320,270 to Crutcher. The drawback of this technique is the problem of coupling the flywheel to the driving anvil. This technique includes the use of a friction clutching mechanism that is complicated, heavy and subject to wear. Further limitation of this approach is the difficulty in controlling the energy in the fastener driving system, as the mechanism requires enough energy to drive the fastener, but retains significant energy in the flywheel after the drive is complete, again increasing the technique complexity and size.
Accordingly, a need exists to provide an electric motor driven device for driving fasteners that is unencumbered by fuel cells or air hoses. What is also needed is a device providing a low reactionary feel and capable of driving full size fasteners, and that is simple in configuration, cost-effective and robust in operation. Further, what is needed is a device that is not fatiguing, is noiseless, portable, and non-hazardous to a user.